Abstract DNA damage-induced cell death through chemo-drugs is the most widely used strategy in cancer therapy. However, selectivity remains a great concern in cancer chemotherapy because DNA damaging drugs kill both cancer cells and the surrounding normal cells, which is an important cause of side effects during cancer chemotherapy, and severely limits current treatment regimes. Functional p53 deficiency is common in human tumors and contributes to an aggressive chemo- or radiotherapy-resistant phenotype, therefore providing a potential target for cancer therapy. Several attempts in recent years to restore wt- p53 activity have led to the identification of numerous p53 modulators. However, strategies mimicking p53 activated transcriptional responses in wt-p53 or p53-deficient tumors have yet to be explored. We carried out a high-throughput cell-based screen for small molecules that trigger a p53 target transcription in cancer cells. Among several candidates that elevate the amounts of p53 proteins, a naturally occurring novel p53 modulator, piperlongumine (PPLGM) is of most interest for this application because it selectively kills cancer cells in both p53-dependent and p53-independent ways, while leaving normal cells unaffected. This compound effectively increases basal levels of p53 protein and its proapoptotic targets. Furthermore, in vivo experiments demonstrate potent anti-tumor activities of this compound at low concentrations, which have no apparent adverse effects on normal organ and tissue function. We also identified significant elevation of reactive oxygen species (ROS) as a potential cancer cell specific mechanism of action for this compound. Therefore, targeting ROS could be a strategy to be developed to selectively kill cancer cells but not untransformed or normal cells by additional ROS production, because cancer cells possess a much higher basal level of ROS in comparison to normal cells. The main goal of this application is to understand the underlying mechanisms for the unusual selective effect of PPLGM in cancer cells in vitro and in vivo. A detailed understanding of the mechanism of action of this compound in both cancer cells and normal cells should provide novel insights into the target based selective therapeutic strategies against cancer, and may also warrant further testing in preclinical and clinical settings.